how do I shrink texture in blender?
There are multiple options of doing what you are asking for.

First option (I'd recommend this one):

You can do this by adding a mapping node and the tweak the Scale values.
The UV texture coordinate is just an example. You can use any input you want, the scaling value will apply for all.



Second option:

When you unwrap an object you can go to the UV/image editor.
Select all faces you want to have a bigger/smaller tiling size and press 'S' to scale the UV's to your liking.